1. Field of the Invention
This invention relates to an optical disk, in which part of the sectors are reproduction-only sectors and remaining sectors are recording-reproduction sectors.
2. Description of the Related Art
For use as an external mass data memory, attention is paid to the reproduction-only optical disk in which data is recorded in the form of pits in submicron size on a plastic disc substrate, and the data is read out by the irradiation of a laser beam converged to a spot of about 1 .mu.m.
The reproduction-only disk is manufactured in such processes of forming sub-micron sized pits modulated by data on the substrate of plastic resin such as polycarbonate with a thickness of 1.2 mm, a reflection layer, e.g., aluminum, is deposited on the resin surface, and a protective layer is applied to the entire surface. A disk with a 12 cm diameter has a storage capacity as much as 500-600 MB, but it does not allow recording of data. The reproduction-only disk will be used by exerting its properties including mass capacity, random access ability, easiness of mass production, and low cost. Examples of conceivable application are dictionaries of word processors, photo-pattern memories, and files of computer programs and instruction manuals.
However, as general characteristics, the optical disk has a high raw error rate as compared with a magnetic disk. On this account, both of data and the error detect-correcting codes are recorded in the process of manufacturing reproduction only disks, and errors of data are detected and corrected using the error detect-correcting codes in the data read-out operation.
An example of error correcting method for the conventional reproduction-only disk apparatus will be described with reference to the drawings.
FIG. 2 shows an example of the recording format. In FIG. 2, indicated by 20 are data, 21 are first error correcting codes, and 22 is the recording direction. Control codes such as a sync code and VFO are omitted in the figure. FIG. 8 is a diagram showing the conventional sector arrangement. In FIG. 8, indicated by 80 is an optical disk and 81 is a reproduction-only sector area.
In this prior example, the error detecting and correcting codes 21 are generated and appended to the data 20 in advance in the record on the optical disk 80. The disk is read out with an optical disk apparatus, and if error is detected in the data, data correction is implemented for the data 20 using the error correcting codes 21. Usually, optical disks are sectored for the sake of easy access.
However, the foregoing scheme necessitates a high-grade error correcting code appended to data so that uncorrectable sectors do not occur, resulting in a longer decoding time and a complex arrangement of the decoder and a reduced data storage capacity due to increased overhead for the code.